Which firewall port needs to be opened between your Network Monitoring System and HPE Aruba...

The correct answer is D. UDP 161. SNMP uses different UDP ports depending on the monitoring function. When a Network Monitoring System collects or polls monitoring data from a CX switch, it communicates with the SNMP agent on the switch. HPE Aruba Networking AOS-CX SNMP documentation shows the SNMP agent port as UDP 161. This is the port used for SNMP polling and monitoring responses. This differs from SNMP traps or alerts, which are sent by the switch to a monitoring system on UDP 162. The question specifically asks about the Network Monitoring System collecting monitoring data from CX switches, so the required firewall allowance is UDP 161 from the monitoring system to the switch. Option A is incorrect because TCP 162 is not the standard SNMP polling port. Option B and option C are incorrect because UDP 1157 and TCP 1156 are not the SNMP polling ports used for this purpose.